Practically every country in the world has agreed to the worldwide pact - Nicaragua didn't agree to the deal in symbolic protest, saying the terms weren't strong enough and calling for richer countries to do more, while the only other non-signee Syria has been in a civil war for almost six years.

Mr Trump, a well-known climate change sceptic, claimed the deal was "negotiated poorly" by Mr Obama and was hurting America, its jobs and people.

But while the US is officially out, three state Governors have created the US Climate Alliance and remain steadfast in upholding the agreement.

New York Governor Andew Cuomo, California Governor Edmund Brown Jr and Washington Governor Jay Insley are the founding members of the alliance. The states collectively represent 68 million people and account for 10 percent of the country's emissions.

In a joint statement, they said the White House's "reckless decision" has "devastating repercussions, not only for the United States, but for the planet".

They accuse the Trump administration of relinquishing leadership and "taking a backseat" to other countries leading the way.

The alliance will "act as a forum to sustain and strengthen existing climate programs, promote the sharing of information and best practices, and implement new programmes to reduce carbon emissions".

Joining them are 68 Mayors from across the country, who are also pledging to meet obligations under the Paris deal. Those cities include Los Angeles, Boston, New York, Houston, Chicago, Seattle, Atlanta, Denver, Miami Beach, New Orleans and Portland.

The 'Climate Mayors' group says they will "continue to lead".

"If the President wants to break the promises made to our allies enshrined in the historic Paris Agreement, we'll build and strengthen relationships around the world to protect the planet from devastating climate risks.

"The world cannot wait - and neither will we."

In his statement, Mr Trump said he was elected "by voters of Pittsbugh, not Paris. I promised I would exit or renegotiate any deal which fails to serve US interests."

That was rebuked by Pittsburgh Mayor Bill Peduto on Twitter, saying 80 percent of the city voted for Hillary Clinton for President.

"Pittsburgh stands with the world and will follow Paris Agreement," he wrote.

Mr Obama says though the White House has rejected the deal, he was confident the country's states, cities and businesses would step up "and do even more to lead the way, and help protect for future generations the one planet we've got".